The present invention relates generally to the field of visual display or magnifying devices of the type for viewing or reading information carried on a microform. More particularly, the invention is directed to such a viewer or reader device which is compact in size and suitable for portable use.
Microform viewers or readers are well known in the art, the most popular of which are the desk or tabletop models which project an image representing the information carried on a microform, onto a rear projection viewing screen. The most common of these desk or tabletop models provides optical systems employing appropriate distances between lenses, mirrors and the screen, so that the image portrayed on the viewing screen will be as near as possible to the full size of the original duplicated on the microform. Because the microform carries the recorded information in a greatly reduced size, magnification to the full original size requires a screen which will accommodate such full size. Additionally, the housing must be sufficiently large to accommodate the required optical path and occlude stray light. Accordingly, such devices have been relatively large in size and unsuitable for portable use. This system does provide many advantages, such as being capable of producing legible, clear and sufficiently enlarged images of the information recorded on the microform for easy viewing. While these devices have generally been successful, their use is limited by their size and does not allow for portability so that the viewer can be carried by the user to any desired location.
Portable microform viewers have been suggested in which the image to be viewed is projected upon a screen, however such devices to reproduce the recorded image at full size are also relatively large and require complicated and expensive folding arrangements to minimize size. These devices also require considerable power in the illumination system to overcome the ambient light in a lighted work area thus requiring a large battery pack for true portable operation.
Other prior art attempts at providing portable microform reader devices have included simple magnifying optical arrangements having a microform holder and a magnifying lens arrangement positioned with respect to the holder so that monocular viewing through the magnifying lens system produces an enlarged virtual image of the reduced information recorded on the microform. This type of device has the advantage of being capable of producing particularly large magnifications of the microform information while maintaining extreme compactness. This type of device, however, suffers from other disadvantages. For example, such systems have severe optical limitations, particularly with respect to the high magnifications and field of view required for normal viewing of microforms. This limitation relates principally to the limitations for eye relief at the viewing lens and the need for accuracy and steadiness with respect to eye alignment along the optical axis. Such disadvantages quickly produce fatigue and discomfort when using such devices.
It is accordingly one object of the present invention to provide a microform reader or viewer of compact dimensions which overcomes many of the disadvantages of the prior art devices.
A further object of the present invention is to provide a microform reader which combines the best features of both the projection or screen viewing type of reader with the magnifying type of reader.
Another object of the present invention is to provide a compact microform reader or viewer which is provided with a viewing screen upon which a real image is projected to an enlarged image, in combination with a magnifying system for producing a further enlarged virtual image.
Yet another object of the present invention is to provide a compact microform reader which is portable, easy to use, will not provide fatigue or difficulty with respect to alignment of the eye along the optical axis, and which requires only a low power magnifying system.
The above objects, features and advantages, along with other objects, features and advantages of the present invention will become more apparent from the detailed description of the invention, in conjunction with the accompanying drawings to be described more fully hereinafter.